Interbody fusion implant

ABSTRACT

An intervertebral implant can include a core and a flexible end plate. The core can have a core body that is elongate along a first direction and defines first and second outer surfaces. The flexible end plate can define an inner surface and an opposed bone facing surface that is configured to abut a vertebral body. The flexible end plate can be coupled to the core such that at least a portion of the inner surface faces the first outer surface and is spaced from the first outer surface. The flexible end plate is configured to resiliently flex toward a compressed configuration such that as the flexible end plate flexes toward the compressed configuration, a first end moves relative to the core along the first direction and the portion of the inner surface moves toward the first outer surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/708,247, filed Oct. 1, 2012, the contents of which are herebyincorporated by reference herein.

BACKGROUND

The placement of a fusion implant within an intervertebral space that isdefined between adjacent vertebral bodies has typically resulted in thefusion of the adjacent vertebral bodies together. This “interbodyfusion” procedure, which is in use today, is a widely accepted surgicaltreatment for symptomatic lumbar and cervical degenerative disc disease(DDD). The aim of a spinal fusion is to relieve pain caused by adegenerated disc, restore anatomy (disc height and/or lordoticcurvature), and immobilize the affected level (fusion).

It has been found that the stiffness of the implants affects the rate ofinterbody fusion and that by reducing the stiffness of the implant therate of interbody fusion can be increased.

SUMMARY

In an embodiment, an intervertebral implant can include a core and anend plate, the core can define a rear end and a front end that is spacedfrom the rear end along an insertion direction. The end plate can definea bone facing surface and an inner surface that is opposite the bonefacing surface, the end plate further defining a first attachment memberand a second attachment member that is spaced from the first attachmentmember, the first and second attachment members being movably coupled tothe core such that at least a portion of the inner surface faces thecore and is spaced from the core a first distance along a firstdirection that is substantially perpendicular to the insertiondirection. The end plate is configured to resiliently move toward thecore along the first direction such that 1) the portion of the innersurface is spaced from the core a second distance along the firstdirection that is less than the first distance, and 2) at least one ofthe first and second attachment members moves along the core.

In an embodiment, an intervertebral implant can include a core and aflexible end plate. The core can have a core body that is elongate alonga first direction and defines first and second outer surfaces that arespaced from each other along a second direction that is perpendicular tothe first direction. The flexible end plate can define an inner surfaceand an opposed bone facing surface that is configured to abut avertebral body. The flexible end plate can be coupled to the core suchthat at least a portion of the inner surface faces the first outersurface and is spaced from the first outer surface by a distance. Theflexible end plate can further define a first end and a second end thatis spaced from the first end along the first direction. The flexible endplate is configured to resiliently flex toward a compressedconfiguration such that as the flexible end plate flexes toward thecompressed configuration, the first end moves relative to the core alongthe first direction and the portion of the inner surface moves towardthe first outer surface such that the distance is decreased.

In an another embodiment, an intervertebral implant can include a firstend plate, a second end plate, and a biasing member coupled between thefirst and second endplates along a first direction. The first end platecan include a first body that defines a first bone facing surface and afirst internal ceiling surface that is opposite the first bone facingsurface along a first direction, the first end plate further includingat least one wall that extends from the first body substantially alongthe direction, wherein the first end plate includes a cavity that is atleast partially defined by the wall and the internal ceiling surface.The second end plate can include a second body that defines a secondbone facing surface, the second body further defining a core having asecond inner surface that is spaced from the second bone facing surfacealong the first direction, the core configured to be received in thecavity such that the second inner surface faces the internal ceilingsurface. The first end plate is configured to move relative to thesecond end plate along the first direction between a first configurationand a second configuration whereby when in the first configuration theinternal ceiling surface is spaced from the second inner surface alongthe first direction by a first distance, and when in the secondconfiguration the internal ceiling surface is spaced from the secondinner surface by a second distance that is less than the first distance,and movement of the first end plate from the first configuration to thesecond configuration causes the biasing member to compress so as to biasthe first end plate along a direction from the second configurationtoward the first configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofillustrative embodiments of the interbody fusion implant of the presentapplication, will be better understood when read in conjunction with theappended drawings. For the purposes of illustrating the intervertebralimplant of the present application, there is shown in the drawingsillustrative embodiments. It should be understood, however, that theapplication is not limited to the precise arrangements and implantsshown. In the drawings:

FIG. 1 is a perspective view of an intervertebral implant positioned inan intervertebral space that is defined between a superior vertebralbody and an inferior vertebral body;

FIG. 2A is a perspective view of an intervertebral implant in accordancewith an embodiment, the implant including a core, a first flexible endplate coupled to a first surface of the core, and a second flexible endplate coupled to a second surface of the core;

FIG. 2B is an exploded perspective view of the intervertebral implantshown in FIG. 2A;

FIG. 2C is a side elevation view of the intervertebral implant shown inFIG. 2A;

FIG. 2D is a top plan view of the intervertebral implant shown in FIG.2A;

FIG. 2E is a front elevation view of the intervertebral implant shown inFIG. 2A;

FIG. 2F is a rear elevation view of the intervertebral implant shown inFIG. 2A;

FIG. 3A is a perspective view of an intervertebral implant in accordancewith another embodiment, the intervertebral implant including a firstend plate that defines a cavity, a second end plate that defines a core,and a biasing member positioned within the first and second end platessuch that as the first end plate moves relative to the second end platefrom an initial configuration toward a compressed configuration, thebiasing member biases the first end plate toward the initialconfiguration;

FIG. 3B is an exploded perspective view of the intervertebral implantshown in FIG. 3A;

FIG. 3C is a side elevation view of the intervertebral implant shown inFIG. 3A;

FIG. 3D is a top plan view of the intervertebral implant shown in FIG.3A;

FIG. 3E is a cross-sectional view of the intervertebral implant shown inFIG. 3A taken through the line 3E-3E;

FIG. 3F is a front elevation view of the intervertebral implant shown inFIG. 3A; and

FIG. 3G is a rear elevation view of the intervertebral implant shown inFIG. 3A;

DETAILED DESCRIPTION

Referring to FIG. 1, a superior vertebral body 10 a defines a first orsuperior vertebral surface 14 a of an intervertebral space 18, and anadjacent second or inferior vertebral body 10 b defines an inferiorvertebral surface 14 b of the intervertebral space 18. Thus, theintervertebral space 18 is disposed between or otherwise defined by thevertebral bodies 10 a and 10 b. The intervertebral space 18 can bedisposed anywhere along the spine as desired, including at the lumbar,thoracic, and cervical regions of the spine. As illustrated, theintervertebral space 18 is illustrated after a discectomy, whereby thedisc material has been removed or at least partially removed to preparethe intervertebral space 18 to receive an intervertebral implant, suchas intervertebral implant 22 that can achieve height restoration forexample as shown in FIG. 1. The intervertebral implant can be configuredas an interbody fusion implant and can be inserted into theintervertebral space 18 along an insertion direction such as from aposterior approach. It should be appreciated, however, that theintervertebral implant 22 can be inserted into the intervertebral space18 along any insertion direction such as from an anterior approach.

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inner” or “distal” and “outer” or “proximal” refer to directionstoward and away from, respectively, the geometric center of the implantand related parts thereof. The words, “anterior”, “posterior”,“superior,” “inferior,” “medial,” “lateral,” and related words and/orphrases are used to designate various positions and orientations in thehuman body to which reference is made and are not meant to be limiting.The terminology includes the above-listed words, derivatives thereof andwords of similar import.

In Reference to FIGS. 2A-2F, the intervertebral implant 22 is describedherein as extending horizontally along a longitudinal direction “L” andlateral direction “A”, and vertically along a transverse direction “T”.Unless otherwise specified herein, the terms “lateral,” “longitudinal,”and “transverse” are used to describe the orthogonal directionalcomponents of various components. It should be appreciated that whilethe longitudinal and lateral directions are illustrated as extendingalong a horizontal plane, and that the transverse direction isillustrated as extending along a vertical plane, the planes thatencompass the various directions may differ during use. For instance,when the intervertebral implant 22 is implanted into the intervertebralspace 18 along an insertion direction I, the transverse direction Textends vertically generally along the superior-inferior (orcaudal-cranial) direction, while the horizontal plane defined by thelongitudinal direction L and lateral direction A lies generally in theanatomical plane defined by the anterior-posterior direction, and themedial-lateral direction, respectively. Accordingly, the directionalterms “vertical” and “horizontal” are used to describe theintervertebral implant 22 and its components as illustrated merely forthe purposes of clarity and illustration.

As shown in FIGS. 2A and 2B, the intervertebral implant 22 can include acore 26 that has a core body 28 that is elongate along a firstdirection, such as along the longitudinal direction L or along theinsertion direction, and defines a first or upper outer surface 30 and asecond or lower outer surface 34 that is spaced from the first outersurface 30 along a second direction that is perpendicular to the firstdirection, such as along the transverse direction T. The intervertebralimplant can further include a first flexible end plate 36 coupled to thefirst outer surface 30 of the core body 28, and a second flexible endplate 38 coupled to the second outer surface of the core body 28. Boththe first flexible end plate 36 and the second flexible end plate 38 areconfigured to resiliently flex toward the core when the intervertebralimplant 22 is inserted into the intervertebral space 18.

As shown in FIGS. 2A-2C, the core body 28 can define a first orposterior or rear end 40 and a second or anterior or front end 44 andcan include a pair of side walls 48 that extend from the posterior end40 to the anterior end 44. The side walls 48 can be spaced from eachother along a third direction, such as along the lateral direction A,such that the core 26 defines a cage. As shown, the side walls 48 extendtoward each other as the side walls 48 extend from the posterior end 40toward the anterior end 44 so as to define a nose 52 at the anterior end44. The core 26 can be rigid and can be made from any suitablebio-compatible material such as metal or plastic. For example the core26 can be made from PEEK or Titanium, as desired.

As shown in FIG. 2B, the core 26 can further include at least one window56 that extends through the core body 28 along the third direction suchas through the side walls 48 along the third direction. In theillustrated embodiment, the core 26 includes two windows 56 that extendthrough the core body 28. It should be appreciated, however, that thecore 26 can include any number of windows 56 and can alternatively bevoid of windows 56 as desired. The windows 56 are configured to promoteboney in-growth. As shown in FIG. 2B, the core 26 can also include atleast one channel 60 that extends through the core body 28 along thesecond direction from the first outer surface 30 to the second outersurface 34. As with the windows 56, the channel 60 is configured to atleast promote boney in-growth.

With continued reference to FIGS. 2A-2F, the first flexible end plate 36defines an inner surface 62 and an opposed bone facing surface 64 thatis configured to abut a vertebral body such as the vertebral body 10 awhen the intervertebral implant is disposed within the intervertebralspace 18. As shown in FIG. 2C, the first flexible end plate 36 can becoupled to core 26 such that at least a portion of the inner surface 62faces the first outer surface 30 and is spaced from the first outersurface 30 by a first distance D₁. The first distance D₁ can be amaximum distance that the inner surface 62 is spaced from the firstouter surface 30 and can be taken at a longitudinal midline of the firstflexible end plate 36 (e.g. halfway between first and second ends of thefirst flexible endplate 36). It should be appreciated, however, that thefirst distance D₁ can be taken at any point along the first flexible endplate 36.

As shown in FIGS. 2B and 2C, the first flexible end plate 36 can definea first or posterior end 70 and a second or anterior end 74 that isspaced from the first end 70 along the first direction. The first andsecond ends 70 and 74 can be coupled to the core body 28 such that thefirst flexible end plate 36 is bowed along the first direction. Theflexible end plate 36 is flexible between a first or initialconfiguration and a second or compressed configuration such that as theend plate 36 flexes toward the compressed configuration the distance D₁is decreased or the at least a portion of the inner surface 62 is spacedfrom the first outer surface 30 by a second distance that is less thanthe first distance D₁. That is, the first flexible end plate 36 isconfigured to resiliently flex toward the compressed configuration suchthat as the flexible end plate flexes toward the compressedconfiguration, the first end 70 moves along the core 26 or at leastrelative to the core 26 along the first direction and the portion of theinner surface 62 that faces the first outer surface 30 moves toward thefirst outer surface 30 such that the distance D₁ is decreased.Similarly, the second end 74 is configured to move along the core 26 orat least relative to the core 26 along the first direction and away fromthe first end 70 when the first flexible end plate 36 flexes toward thecompressed configuration. When in the initial configuration the distanceD₁ can be between about 0.5 mm and about 10.0 mm and when in thecompressed configuration the second distance can be about 0.0 mm. Itshould be appreciated, however, that the first and second distances canbe any number as desired when the first flexible end plate 36 is in theinitial configuration or in the compressed configuration. Moreover, itshould be appreciated, that while in the illustrated embodiment both thefirst and second ends 70 and 74 are configured to move along the firstdirection, in certain embodiments one of the first and second ends 70and 74 can be fixed.

As shown in FIG. 2D, the first and second ends 70 and 74 of the firstflexible end plate 36 can include first and second attachment members 79a and 79 b such that the attachment members can be movably coupled tothe core body 28 proximate to the posterior and anterior ends 40 and 44of the core body 28. As shown, the first and second attachment members79 a and 79 b can define first and second slots 80 a and 80 b,respectively, which are elongate along the first direction and arecarried by the first and second ends 70 and 74, respectively. As shownin FIG. 2B, implant 22, or at least the core 26 of the implant, caninclude first and second fixation members 82 a and 82 b that extendthrough the first and second slots 80 a and 80 b and into the firstouter surface 30 of the core body 28 to thereby couple the firstflexible end plate 36 to the core body 28. The first flexible end plate36 can be coupled to the core body 28 such that the first and secondfixation members 82 a and 82 b limit the movement of the first andsecond ends 70 and 74 of the end plate 36 along the first direction whenthe flexible end plate 36 flexes toward the compressed configuration.

As shown in FIG. 2B, the first and second fixation members 82 a and 82 bcan be pins that couple to the core body 28 through an interference fit.For example, the fixation members 82 a and 82 b can include a shaft 84and a head 86 that extends out from an end of the shaft 84. The head 86can be configured to have a dimension that is greater than that of alateral dimension of the slots 80 a and 80 b and the shaft 84 can beconfigured to have a dimension that is less than the lateral dimensionof the slots 80 a and 80 b. Therefore, the first and second ends 70 and74 can be coupled to the core body 28 while at the same time be capableof translating along the first direction. It should be appreciated,however, that the fixation members 82 a and 82 b can have anyconfiguration as desired. For example, the fixation members 82 a and 82b can be threaded. Moreover, it should be appreciated that the first andsecond ends 70 and 74 can be coupled to the core body 28 with structureother than fixation members. For example, the core body 28 can defineslots that are configured to translatably receive the first and secondends 70 and 74.

As shown in FIG. 2D, the first flexible end plate 36 can define a middleregion 89 that extends from the first attachment member 79 a to thesecond attachment member 79 b. The first flexible end plate 36 caninclude at least one channel 90 that extends through the middle region89 from the inner surface 62 to the bone facing surface 64 such that theat least one channel 60 of the core 26 and the at least one channel 90of the flexible end plate 36 are substantially aligned along the seconddirection. The aligned channels 60 and 90 can help promote boneyin-growth after the implant 22 has been inserted into the intervertebralspace 18. Furthermore, the flexible end plate 36 can define a pluralityof teeth 94 that extend out from the bone facing surface 64. The teeth94 can be configured to prevent migration of the intervertebral implant22 after the implant 22 has been inserted into the intervertebral space18.

As the first and second ends slide along the core 26, an entirety of themiddle region 89 can be spaced from the core 26 along the firstdirection. It should be appreciated, however, that in some embodiments,as the first and second ends slide along the core 26 portions of themiddle region 89 can be in contact with the core 26. Moreover, it shouldbe appreciated, that while the first and second attachment members 79 aand 79 b or at least the first and second ends 70 and 74 are illustratedas sliding along the first outer surface 30, the first and secondattachment members 79 a and 79 b or at least the first and second ends70 and 74 can slide along inner surfaces defined by the core 26.

With continued reference to FIGS. 2A-2F, the second flexible end plate38 can be substantially identical to the first flexible end plate 36 andcan include like structure unless otherwise described. It should beappreciated, however, that while in the illustrated embodiment the firstand second flexible end plates 36 and 38 are substantially identical,the end plates 36 and 38 can include different structure and havedifferent shapes as desired.

As shown in FIG. 2B, the second flexible end plate 38 defines an innersurface 162 and an opposed bone facing surface 164 that is configured toabut a vertebral body such as vertebral body 10 b. As shown in FIG. 2C,the second flexible end plate 38 can be coupled to core 26 such that atleast a portion of the inner surface 162 faces the second outer surface34 and is spaced from the second outer surface 34 by a third distanceD₂. The third distance D₂ can be a maximum distance that the innersurface 162 is spaced from the second outer surface 34 and can be takenat a longitudinal midline of the second flexible end plate 38 (e.g.halfway between first and second ends of the second flexible endplate38). It should be appreciated, however, that the second distance D₂ canbe taken at any point along the second flexible end plate 38, asdesired.

As shown in FIG. 2C, the second flexible end plate 38 can define a firstor posterior end 170 and a second or anterior end 174 that is spacedfrom the first end 170 along the first direction. The first and secondends 170 and 174 can be coupled to the core body 28 such that the secondflexible end plate 38 is bowed along the first direction. The flexibleend plate 38 is flexible between a first or initial configuration and asecond or compressed configuration whereby the distance D₂ is decreasedor the at least a portion of the inner surface 162 is spaced from thesecond outer surface 34 by a fourth distance that is less than the thirddistance. That is, the second flexible end plate 38 is configured toresiliently flex toward the compressed configuration such that as theflexible end plate flexes toward the compressed configuration, the firstend 170 moves relative to the core 26 along the first direction and theportion of the inner surface 162 moves toward the second outer surface34 such that the distance D₂ is decreased. Similarly, the second end 174is configured to move relative to the core 26 along the first directionand away from the first end 170 when the second flexible end plate 38flexes toward the compressed configuration. When in the initialconfiguration the third distance D₂ can be between about 0.5 mm andabout 10.0 mm and when in the compressed configuration the fourthdistance can be about 0.0 mm. It should be appreciated, however, thatthe third and fourth distances can be any number as desired when thesecond flexible end plate 38 is in the initial configuration or in thecompressed configuration. Moreover, it should be appreciated, that whilein the illustrated embodiment both the first and second ends 170 and 174are configured to move along the first direction, in certain embodimentsone of the first and second ends 170 and 174 can be fixed.

As shown in FIG. 2B, the first and second ends 170 and 174 of the secondflexible end plate 38 can be moveably coupled to the core body 28proximate to the posterior and anterior ends 40 and 44 of the core body28. As shown, the second flexible end plate 38 can include first andsecond attachment members 179 a and 179 b such that the attachmentmembers can be movably coupled to the core body 28 proximate to theposterior and anterior ends 40 and 44 of the core body 28. As shown, thefirst and second attachment members 179 a and 179 b can define first andsecond slots 180 a and 180 b that are elongate along the first directionand located proximate to the first and second ends 70 and 74,respectively. As shown in FIG. 2B, the core 26 can include third andfourth fixation members 182 a and 182 b that extend through the firstand second slots 180 a and 180 b and into the second outer surface 34 ofthe core body 28 to thereby couple the second flexible end plate 38 tothe core body 28 such that the third and fourth fixation members 182 aand 182 b limit the movement of the first and second ends 170 and 174along the first direction when the flexible end plate 38 flexes towardthe compressed configuration.

It should be appreciated that while the first flexible end plate 36 iscoupled to the core body 28 with first and second fixation members 82 aand 82 b and the second end plate 38 is coupled to the core body 28 withthird and fourth fixation members 182 a and 182 b, the first and secondflexible end plates 36 and 38 can be coupled to the core body 28 using afirst fixation member that extends through the core body 28 and throughboth first slots 80 a and 180 a, and a second fixation member thatextends through the core body and through both second slots 80 b and 180b.

The first and second flexible end plates 36 and 38 can be made from anybio-compatible material as desired. For example, the first and secondflexible end plates 36 and 38 can be made from a bio-compatible metalsuch as Titanium, Steel, or any material that can provide spring-action.The first and second end plates 36 and 38 can also have a stiffness thatis configured to support or otherwise match the stiffness of thevertebral bodies 10 a and 10 b. For example, the modulus of elasticityof cortical bone is between 7 and 30 GPa and the first and secondendplates 36 and 38 can have a stiffness that is configured to supportthis range of moduli. Therefore, the first and second endplates 36 and38 can have a stiffness that is between about 7 GPa and about 30 GPA. Itshould be appreciated, however, that the first and second end plates 36and 38 can have any stiffness as desired. For example, the modulus ofelasticity of cancellous bone is 55.6 MPa and the first and second endplates 36 and 38 can have a stiffness that is about 55.6 MPa to therebymatch the stiffness of the cancellous bone in the rare case that thecortical bone is lost and the cancellous bone is exposed. It should beappreciated, that the stiffness of the end plates 36 and 38 can bedependent on a variety of factors such as the material choice and thegeometry of the end plates 36 and 38.

The implant 22 can be sold individually or as a kit that includes thecore 26, a plurality of flexible end plates 36 and 38, and a pluralityof fixation members. At least one of the end plates 36 and 38 can have astiffness that is different than the stiffness of at least one of theother flexible end plates. It should be appreciated, however, that someof the end plates of the plurality of end plates can have the samestiffness. Moreover, it should be appreciated, that the end plates ofthe plurality of end plates can have different shapes, be made fromdifferent materials, and/or have different coupling features.

Now in reference to FIGS. 3A-3F, an intervertebral implant 222 inaccordance with another embodiment can include a first end plate 226, asecond end plate 230 coupled to the first end plate 226, and a biasingmember 234 coupled between the first and second end plates 226 and 230along a first direction. The first end plate 226 is configured to moverelative to the second end plate 230 along the first direction, such asalong the transverse direction, between an initial or firstconfiguration and a compressed or second configuration and movement ofthe first end plate from the first configuration to the secondconfiguration causes the biasing member 234 to compress so as to biasthe first end palate along the first direction from the secondconfiguration toward the first configuration.

As shown in FIGS. 3A-3E, the first end plate 226 includes a first body240 that is elongate along a second direction, such as along thelongitudinal direction or insertion direction. The first body 240defines a first bone facing surface 244 and a first inner or internalceiling surface 248 that is spaced from the first bone facing surface244 along a first direction, such as along the transverse direction. Thefirst body 240 can define a first or posterior end 252 and a second oranterior end 256. The first end plate 226 can further include at leastone wall that extends from the first body 240 substantially along thefirst direction. For example, the first end plate 226 can include a pairof side walls 260 that extend from the posterior end 252 to the anteriorend 256. The side walls 260 can extend toward each other as the sidewalls 260 extend from the posterior end 252 toward the anterior end 256so as to define a nose 258 at the anterior end 256. The side walls 260can be spaced from each other along a third direction, such as along thelateral direction A, such that the posterior end 252, the anterior end256, and the side walls 260 define a cavity 264 of the first body.Therefore, the at least one wall can be a single continuous wall thatincludes the posterior end 252, anterior end 256, and side walls 260such that the cavity 264 is at least partially defined by the at leastone wall and the internal ceiling surface 248.

In particular, the cavity 264 can be defined by a first pair of internalside surfaces 272 that are spaced along the second direction, and asecond pair of internal side surfaces 276 that are spaced along thethird direction. As shown, the internal side surfaces 272 of the firstpair of side surfaces 272 are spaced from each other along the firstdirection by a distance D₃. The distance D₃ can be any dimension asdesired so long as the cavity 264 can receive a portion of the secondend plate 230.

As shown in FIG. 3E, the first end plate 226 further includes a recess280 that extends into the internal ceiling surface 248 and toward thefirst bone facing surface 244. The recess 280 can be configured as abore as illustrated and can be configured to receive a portion of thebiasing member 234. It should be appreciated, however, that the recess280 can have any configuration as desired. For example, the recess 280can be substantially cubed shaped. Moreover, it should be appreciated,that the end plate 226 can include multiple recesses 280 if desired.

With continued reference to FIGS. 3A-3E, the second end plate 230includes a second body 340 that is elongate along the second direction,such as along the longitudinal direction. As shown, the second body 340defines a second bone facing surface 344 and a second inner surface 348that is spaced from the second bone facing surface 344 along the firstdirection, such as along the transverse direction. The second body 340can define a first or posterior end 352 and a second or anterior end 356that is spaced form the posterior end 352 along the second direction. Atleast a portion of the second body 340 defines a core 364 that isconfigured to be received by the cavity 264 of the first body 240 suchthat the internal ceiling surface 248 faces the second inner surface348. Therefore, the core 364 can be said to define the second innersurface 348.

The core 364 can define a first pair of external side surfaces 368 thatare spaced along the second direction and a second pair of external sidesurfaces 372 that are spaced along the third direction. The second pairof side surfaces 372 extend toward each other as the side surfaces 372extend from the posterior end 352 toward the anterior end 356 such thatthe core 364 defines a nose 370 at the anterior end 356. The externalside surfaces 368 of the first pair of external side surfaces 368 arespaced from each other along the first direction by a distance D₄. Thedistance D₄ can be substantially equal to the distance D₃ such that thecore 364 can be received within the cavity 264. It should beappreciated, however, that the distance D₄ can be any dimension asdesired so long as the cavity 264 can receive the core 364 of the secondend plate 230. Moreover, it should be appreciated that while in theillustrated embodiment the core 364 has shape that is substantiallyidentical to that of the cavity 264, in certain embodiments the shapesof the core and the cavity can be different so long as the cavity canreceive the core.

The anterior and posterior ends 252 and 256 can trap the core 364 withinthe cavity 264. Therefore, the anterior and posterior ends 252 and 256can be said to be first and second attachment members. As the core 364moves within the cavity 264, the first and second attachment membersmove or otherwise will slide along the core along the first direction.

As shown in FIGS. 3B and 3E, the second end plate 230 can furtherinclude a shoulder 380 that extends out from the second body 340 suchthat the shoulder 380 defines an abutment surface 384 that faces an end385 of the at least one wall. The shoulder 380 can be configured tolimit movement of the first end plate 226 relative to the second endplate 230 along the first direction when the end 385 abuts the abutmentsurface 384. The shoulder 380 can extend completely around the secondbody 340 and can be continuous as illustrated or the shoulder 380 can besegmented as desired. It should be appreciated, however, that in certainembodiments, the internal ceiling surface 248 can abut the second innersurface 348 to thereby limit the movement of the first end plate 226relative to the second end plate 230 along the first direction.

As shown in FIG. 3E, the second end plate 230 further includes a recess392 that extends into the second inner surface 348 and toward the secondbone facing surface 344. The recess 392 can be configured as a bore asillustrated and can be configured to receive a portion of the biasingmember 234. It should be appreciated, however, that the recess 392 canhave any configuration as desired. For example, the recess 392 can besubstantially cubed shaped. Moreover, it should be appreciated, that thesecond end plate can include any number of recesses 392 as desired.

The first and second end plates 226 and 230 can be made from anybio-compatible material such as PEEK and/or Titanium. Furthermore, atleast one of the first end plate 226 and the second end plate 230 caninclude a radio-opaque marker 398 that is configured to indicate theposition of the implant during implantation. In the illustratedembodiment, the first end plate 226 includes one marker 398 and thesecond end plate 230 includes two markers 398. It should be appreciated,however, that the first and second end plates 226 and 230 can includeany number of markers 398 as desired, in any direction as desired, andof any shape (e.g. pin, ball, etc) as desired.

Furthermore, the first and second end plates 226 and 230 can define aplurality of teeth 400 that extend out from the bone facing surfaces 244and 344. The teeth 400 can be configured to prevent migration of theintervertebral implant 222 after the implant 222 has been inserted intothe intervertebral space 18. Moreover, it should be appreciated that thefirst and second endplates 226 and 230 can define channels and windowssimilar to those of the implant 22 to thereby further promote boneyin-growth.

As shown in FIGS. 3B and 3E, the biasing member 234 can be positioned inthe recesses 280 and 392 of the first and second end plates 226 and 230.Therefore, the recess 280 of the first end plate 226 can be coaxial withthe recess 392 of the second end plate 230 when the core 364 is receivedby the cavity 264 such that the biasing member 234 is trapped within therecesses 280 and 392. The biasing member 234 can be a spring such as acircular compression spring as illustrated. It should be appreciated,however, that the biasing member 234 can have any configuration asdesired. For example, the biasing member 234 can be configured as asolid compression member.

The biasing member 234 can have a stiffness that is configured tosupport or otherwise match the stiffness of the vertebral bodies 10 aand 10 b. For example, the modulus of elasticity of cortical bone isbetween 7 GPa and 30 GPa and the biasing member 234 can have a stiffnessthat is configured to support this range of moduli. Therefore, thebiasing member 234 can have a stiffness that is between about 7 GPa andabout 30 GPA. It should be appreciated, however, that the biasing member234 can have any stiffness as desired. For example, the modulus ofelasticity of cancellous bone is 55.6 MPa and the biasing member 234 canhave a stiffness of about 55.6 MPa.

As shown in FIG. 3E, when the first end plate 226 is coupled to thesecond end plate 230 at least one of the first end plate 226 and thesecond end plate 230 is configured to move relative to the other alongthe first or transverse direction between an initial or firstconfiguration and a compressed or second configuration. When in theinitial configuration, the internal ceiling surface 248 is spaced fromthe second inner surface 348 along the first direction by a firstdistance d₁. When in the compressed configuration, the internal ceilingsurface 248 is spaced from the second inner surface 348 along the seconddirection by a second distance d₂ that is less than the first distanced₁. Therefore, it can be said that when the first end plate 226 movestoward the compressed configuration, the first distance d₁ decreases.The first distance d₁ can between about 0.5 mm and about 10.0 mm and thesecond distance d₂ can be about 0 mm. It should be appreciated, however,that the first and second distances d₁ and d₂ can be any distances asdesired.

When in the compressed configuration, the biasing member 234 isconfigured to bias the first end plate 226 toward the initialconfiguration. It should be appreciated, however, that the implant 222can include more than one biasing member 234 as desired. For example,the implant 222 can include two biasing members that bias the first endplate 226 toward the initial configuration.

The first and second end plates 226 and 230 can be coupled together bythe biasing member 234 or the at least one side wall can include fingersthat engage the core so as to allow the core to move within the cavityalong the first direction. It should be appreciated, however, that thefirst and second end plates 226 and 230 can be coupled together usingany structure as desired so long as the core is capable of moving alongthe first direction within the cavity.

When the implant 22 or the implant 222 is inserted into theintervertebral space 18 the implants 22 and 222 can substantially matchthe stiffness of the vertebral bodies 10 a and 10 b to thereby promotefusion. Because of the construction of the implants 22 and 222, theimplants 22 and 222 can be customized to match a variety of stiffnesses.Therefore, it can be said that in some embodiments the implants 22 and222 are customizable or have adjustable stiffnesses. It should beappreciated, however, that the implants 22 and 222 can be constructed tohave a specified stiffness.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be understood that variousadditions, modifications, combinations and/or substitutions may be madetherein without departing from the spirit and scope of the invention asdefined in the accompanying claims. In particular, it will be clear tothose skilled in the art that the invention may be embodied in otherspecific forms, structures, arrangements, proportions, and with otherelements, materials, and components, without departing from the spiritor essential characteristics thereof. One skilled in the art willappreciate that the invention may be used with many modifications ofstructure, arrangement, proportions, materials, and components, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the invention. Inaddition, features described herein may be used singularly or incombination with other features. For example, features described inconnection with one embodiment may be used and/or interchanged withfeatures described in another embodiment. The presently disclosedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, and not limited to the foregoingdescription.

It will be appreciated by those skilled in the art that variousmodifications and alterations of the invention can be made withoutdeparting from the broad scope of the appended claims. Some of thesehave been discussed above and others will be apparent to those skilledin the art.

What is claimed:
 1. An intervertebral implant comprising: a coredefining a rear end and a front end that is spaced from the rear endalong an insertion direction; an end plate that defines a bone facingsurface having a plurality of teeth extending outwardly therefrom and aninner surface that is opposite the bone facing surface along a firstdirection, substantially perpendicular to the insertion direction, theend plate defining a first end including a first attachment member, andthe end plate defining a second end that is spaced from the first end,the second end including a second attachment member that is spaced fromthe first attachment member, the first and second attachment membersbeing movably coupled to the core such that at least a portion of theinner surface faces a surface of the core, such that the portion isspaced from the surface of the core a first distance along the firstdirection, and so as to bias the portion of the inner surface away fromthe surface of the core, wherein the end plate is resiliently movabletoward the core along the first direction without causing movement ofthe core such that 1) the portion of the inner surface is spaced fromthe surface of the core a second distance along the first direction thatis less than the first distance, and 2) at least one of the first andsecond ends is in contact with the surface of the core as the at leastone of the first and second ends slides along the surface of the core.2. The intervertebral implant of claim 1, wherein the first and secondattachment members are spaced along a second direction that issubstantially perpendicular to the first direction, and the at least oneof the first and second attachment members moves along the core alongthe second direction.
 3. The intervertebral implant of claim 2, whereinthe second direction coincides with the insertion direction.
 4. Theintervertebral implant of claim 3, wherein the end plate is flexible soas to resiliently move toward the core along the first direction.
 5. Theintervertebral implant of claim 1, wherein the first and second endscarry the first and second attachment members, respectively, the coredefines first and second outer surfaces, and at least one of the firstand second ends is configured to slide along a respective one of thefirst and second outer surfaces.
 6. The intervertebral implant of claim5, wherein the endplate defines a middle region that extends from thefirst attachment member to the second attachment member, and the firstand second ends slide along the core when an entirety of the middleregion is spaced from the core along the first direction.
 7. Theintervertebral implant of claim 1, wherein the at least one of the firstand second attachment members moves along the core along the firstdirection.
 8. An intervertebral implant comprising: a core having a corebody that defines first and second outer surfaces that are spaced fromeach other along a first direction, the core body being elongate along asecond direction that is perpendicular to the first direction; and aflexible end plate that defines an inner surface and a bone facingsurface that is spaced from the inner surface along the first direction,the flexible end plate being coupled to the core such that at least aportion of the inner surface faces the first outer surface and is spacedfrom the first outer surface by a first distance, the flexible end platefurther defining a first end configured to couple to the core and asecond end configured to couple to the core, the second end spaced fromthe first end along the second direction, wherein, when the first andsecond ends are coupled to the core, the flexible end plate isconfigured to resiliently flex toward the core such that, as theflexible end plate flexes, 1) the first end moves relative to the corealong the second direction, 2) the second end moves relative to the corealong the second direction and away from the first end, and 3) theportion of the inner surface moves toward the first outer surface suchthat the at least a portion of the inner surface is spaced from thefirst outer surface by a second distance that is less than the firstdistance.
 9. The intervertebral implant of claim 8, wherein the flexibleend plate defines first and second slots that are elongate along thesecond direction, the first slot is located proximate to the first endand the second slot is located proximate to the second end, and the coreincludes first and second fixation members that are supported by thecore body and extend through the first and second slots, respectively,to thereby couple the flexible end plate to the core body such that thefirst and second fixation members limit the movement of the first andsecond ends along the second direction when the flexible end plateflexes toward the core.
 10. The intervertebral implant of claim 9,wherein the first and second fixation members are pins that extend fromthe core body.
 11. The intervertebral implant of claim 10, wherein thepins couple to the core body through an interference fit.
 12. Theintervertebral implant of claim 8, wherein the flexible end plate is afirst flexible end plate and the intervertebral implant furthercomprises a second flexible end plate that is coupled to the core suchthat at least a portion of an inner surface of the second flexible endplate faces the second outer surface and is spaced from the second outersurface by a third distance.
 13. The intervertebral implant of claim 12,wherein the second flexible end plate is configured to resiliently flextoward the core such that as the second flexible end plate flexes, afirst end of the second flexible end plate moves relative to the corealong the second direction and the portion of the inner surface of thesecond end plate moves toward the second outer surface such that the atleast a portion of the inner surface of the second end plate is spacedfrom the second outer surface by a fourth distance that is less than thethird distance.
 14. The intervertebral implant of claim 8, wherein theflexible end plate is made of a bio-compatible metal.
 15. Theintervertebral implant of claim 8, wherein the flexible end plate has astiffness that is between about 7 GPa and about 30 GPa.
 16. Theintervertebral implant of claim 8, wherein the core includes at leastone window that extends through the core body along a third directionthat is transverse to the first and second directions.
 17. Theintervertebral implant of claim 8, wherein the core includes at leastone channel that extends through the core body along the firstdirection, and the flexible end plate defines at least one channel thatextends through the flexible end plate from the inner surface to thebone facing surface such that the at least one channel of the core andthe at least one channel of the flexible end plate are substantiallyaligned along the first direction.
 18. The intervertebral implant ofclaim 8, wherein the first and second distances are measured at alocation halfway between the first and second ends.
 19. Theintervertebral implant of claim 18, wherein the flexible end plate isconfigured to have an initial configuration that defines the firstdistance and a compressed configuration that defines the seconddistance, and the flexible end plate is configured to flex between theinitial configuration and the compressed configuration.
 20. Theintervertebral implant of claim 19, wherein the second distance is about0 mm when the flexible end plate is in the compressed configuration. 21.The intervertebral implant of claim 20, wherein the flexible end plateis bowed along the second direction when in the initial configuration.22. The intervertebral implant of claim 19, wherein the first distanceis between about 0.5 mm and about 10.0 mm when the flexible end plate isin the initial configuration.
 23. The intervertebral implant of claim 8,wherein the flexible end plate defines a plurality of teeth that extendout from the bone facing surface.
 24. A kit comprising: a core having acore body that is elongate along a first direction, defines a rear endand a front end that is spaced from the rear end along the firstdirection, and defines a pair of outer surfaces that are spaced fromeach other along a second direction that is perpendicular to the firstdirection; and a plurality of flexible end plates, each flexible endplate defining an inner surface and an opposed bone facing surface, eachflexible end plate being configured to attach to the core at a firstattachment and a second attachment spaced from the first attachmentalong the first direction such that each flexible end plate is bowedalong the first direction and at least a portion of the inner surface ofeach flexible end plate faces one of the outer surfaces, such that thefirst and second attachments limit movement of the flexible end platesalong the first direction both towards and away from the front end ofthe core, and so as to bias at least a portion of the flexible endplates away from the core along the first direction.
 25. The kit ofclaim 24, wherein each flexible end plate defines a first end and asecond end that is spaced from the first end along the first direction,and each flexible end plate that is coupled to the core is configured toresiliently flex toward a compressed configuration such that as theflexible end plates flex toward the compressed configuration, the firstand second ends of the flexible end plates move away from each otherrelative to the core and along the first direction.
 26. The kit of claim24 further comprising a plurality of pins that are configured to couplethe flexible end plates to the core.
 27. The kit of claim 24, wherein atleast one of the flexible end plates has a stiffness that is differentthan the stiffness of at least one of the other flexible end plates. 28.The kit of claim 24, wherein at least one of the flexible end platesdefines a plurality of teeth that extend out from the bone facingsurface.